Kay, M. H., "An assessment of the CODASYL DDL for use with a relational sub-schema" pp199-214.

[IFIP] Proc. of IFIP TC-2 Special Working Conf., (1972) [IFIP] Proc. of IFIP TC-2 Special Working Conf., "An In-depth Technical Evaluation of the CODASYL DDL" 1972  

Languages mentioned DDL {1972} CODASYL Data Definition Language